The invention relates broadly to occupancy sensors and more specifically to a single technology micro-motion occupancy sensor system that is sufficiently sensitive to identify a presence of a sedentary person in a room in order to control electrical power delivery to the room.
Occupancy sensors were developed to determine when a person is in a predetermined volumetric space and supply electrical power thereto only if one or more persons are present. Typically, some fixed time after a last presence in the space is detected (e.g., using a motion sensor), an electrical power delivery circuit to the space is opened, which cuts off all appliances and fixtures connected thereto from the electrical supply. One of the shortcomings of known occupancy sensors, however, is that they miss a presence of sedentary persons.
As used herein, predetermined volumetric space is meant to convey a space that is covered by an occupancy sensor system, such as an enclosed space or room, a portion of an enclosed space or room, or an open space having a volumetric extent covered by the occupancy sensor or occupancy sensor system (referred to interchangeably herein as space, volume or room).
Many known occupancy sensor systems include and rely upon a Passive Infrared (PIR) motion sensor to identify occupants of a room or space. PIR motion sensor systems detect or identify a person's presence when the person (or persons) move in front of the sensor receiver, or pass the sensor system receiver. Such movement in front of the sensor receiver results in an increase in the amount of IR energy received at the time of the movement, i.e., the presence adds IR energy to the ambient IR energy of the passive IR beam received by the sensor system. But as suggested above, such known PIR occupancy sensor systems can miss a presence of a sedentary person, typically because when “covering” a large volumetric space or room, conventional PIR occupancy sensor systems fail to detect “small” motions of a substantially sedentary person. The phrases “small motions” or “substantially sedentary” should be interpreted herein as motions of parts of a person who is not moving from one location to another, for example, writing or inputting data through a computer or cell phone keyboard or other input device.
Again, many conventional PIR occupancy sensor systems, particularly based on direction of the receiving port, are unable to detect small motions of a substantially sedentary person because the small motion does not cross one of the passive IR beams. Hence, if the occupancy sensor system is used to control a light, for example, and the person is sitting at a desk, the power to the light will be interrupted after a fixed time (typically set by the manufacturer) and the light will turn off. In order to have the light turned back on, the person would have to move a sufficient amount to cross one of the passive beams of the occupancy sensor system and wave their hands in some circumstances, actually stand up from his/her chair and walk to or past the conventional PIR occupancy sensor system.
Attempted solutions to this problem are known. One attempted solution relies upon a use of dual technology: a passive infrared motion sensor system and a Doppler acoustic sensor. The Doppler sensor, which operates as a sonar (sound navigation and ranging) system, is capable of detecting minimal human motion. Use of Doppler sensors, however, comes with its own problems. For example, Doppler sensors have a tendency to occasionally raise false alarms and perhaps as importantly, there is an additional cost associated with adding the Doppler sensor as they require additional transmit/receive transducer(s), amplification and detection circuitry and a controller programmed to orchestrate the system operation.